diff --git a/debug/debug.py b/debug/debug.py
index 29db8fc..9edb195 100644
--- a/debug/debug.py
+++ b/debug/debug.py
@@ -17,7 +17,7 @@ os.environ['disable_checks'] = 'true'
 with open(pwd + "/../mach_nix/provider_defaults.toml") as f:
     provider_settings = toml.load(f)
 provider_settings.update(dict(
-    _default="wheel,nixpkgs,sdist",
+    _default="wheel,sdist,nixpkgs",
 ))
 os.environ['providers'] = json.dumps(provider_settings)
 
diff --git a/debug/pypi-deps-db.nix b/debug/pypi-deps-db.nix
index a4b0cb5..e9525a9 100644
--- a/debug/pypi-deps-db.nix
+++ b/debug/pypi-deps-db.nix
@@ -1,5 +1,5 @@
 let
-  pkgs =  import (import ../mach_nix/nix/nixpkgs-src.nix).stable {};
+  pkgs =  import (import ../mach_nix/nix/nixpkgs-src.nix) {};
   commit = builtins.readFile ../mach_nix/nix/PYPI_DEPS_DB_COMMIT;
   sha256 = builtins.readFile ../mach_nix/nix/PYPI_DEPS_DB_SHA256;
   src = builtins.fetchTarball {
diff --git a/mach_nix/data/providers.py b/mach_nix/data/providers.py
index 34ed1b7..38fd4a7 100644
--- a/mach_nix/data/providers.py
+++ b/mach_nix/data/providers.py
@@ -233,12 +233,6 @@ class NixpkgsDependencyProvider(DependencyProviderBase):
             return [p.ver for p in self.nixpkgs.get_all_candidates(name)]
         return []
 
-    # def unify_key(self, key: str) -> str:
-    #     key = super(NixpkgsDependencyProvider, self).unify_key(key)
-    #     if key in self._aliases:
-    #         return self._aliases[key]
-    #     return key
-
 
 class WheelDependencyProvider(DependencyProviderBase):
     name = 'wheel'
@@ -408,8 +402,11 @@ class SdistDependencyProvider(DependencyProviderBase):
                 reqs_raw = pkg[t]
                 reqs = parse_reqs(reqs_raw)
                 requirements[t] = list(filter_reqs_by_eval_marker(reqs, self.context))
-        if extras:
-            requirements['install_requires'] += self.get_reqs_for_extras(pkg_name, pkg_version, extras)
+        if not extras:
+            extras = []
+        # even if no extras are selected we need to collect reqs for extras,
+        # because some extras consist of only a marker which needs to be evaluated
+        requirements['install_requires'] += self.get_reqs_for_extras(pkg_name, pkg_version, extras)
         return requirements['install_requires'], requirements['setup_requires']
 
     def _available_versions(self, pkg_name: str) -> Iterable[Version]:
diff --git a/mach_nix/generators/overlay_generator.py b/mach_nix/generators/overlay_generator.py
index e806c81..bdbbce5 100644
--- a/mach_nix/generators/overlay_generator.py
+++ b/mach_nix/generators/overlay_generator.py
@@ -26,9 +26,7 @@ class OverlaysGenerator(ExpressionGenerator):
         super(OverlaysGenerator, self).__init__(*args, **kwargs)
 
     def generate(self, reqs) -> str:
-        pkgs = self.resolver.resolve(
-            reqs,
-        )
+        pkgs = self.resolver.resolve(reqs)
         pkgs = dict(sorted(((p.name, p) for p in pkgs), key=lambda x: x[1].name))
         return self._gen_python_env(pkgs)